A UK official said that Russia asking to be involved in the investigation of the Salisbury nerve agent attack is akin to an arsonist “investigating his own fire”. 

If the Skripal incident were handled like an NHS complaint by PHSO it would go something like this:

UK: Hi Russia, sorry to bother you but we have had a complaint that your chaps have used a highly toxic nerve agent to assassinate a citizen on UK soil.  This is in breach of the Geneva protocol and in direct contradiction to the UN Convention on the storage and distribution of toxic chemicals. What do you have to say?

Russia: As you know our legal team have already been through all the evidence regarding this complaint as part of the first-tier complaint handling process. We can confirm that this accusation is entirely without merit.  Also, both the Geneva protocol and the UN Convention are only guidelines so I can assure you that there have been no breaches on our part.

UK:  Thanks for the confirmation Russia.  Are we able to see the evidence you relied upon to make your decision that no breaches occurred?

Russia: Unfortunately, we are just in the process of updating our IT systems and the official record is unavailable at this time. We would be happy to provide you with our expert witness statement but this is personal information which belongs to the individual and we must protect his confidentiality.  We take complainants of this nature very seriously and I give you my word that our investigation has been both robust and thorough.

UK: That’s fine. You will be in receipt of our draft report in the next few days and the final report the day after that and we are happy to confirm no uphold. See you at the next UN conference in Geneva?

Russia: Absolutely, I owe you a coffee. Cheers.